CN101133579A

CN101133579A - OFDM communication system and OFDM communication method

Info

Publication number: CN101133579A
Application number: CNA2005800488480A
Authority: CN
Inventors: 关宏之
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2005-03-02
Filing date: 2005-03-02
Publication date: 2008-02-27
Anticipated expiration: 2025-03-02
Also published as: US20070297323A1; JPWO2006092852A1; KR100959207B1; KR20090034407A; EP1855403A1; CN101133579B; US7839880B2; EP1855403A4; JP4476324B2; WO2006092852A1

Abstract

In an OFDM communication system for performing OFDM data communication by dividing a band into a plurality of bands and allotting each band to a mobile station, transmission characteristics of the band and the use status of the adjacent bands are monitored, and based on such information, whether a guard band area provided at a boundary of the bands is to be used for data transmission or not as the guard band for data transmission is decided.

Description

OFDM communication system and OFDM communication method

Technical Field

The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) communication system and an OFDM communication method, and more particularly to a base station of an OFDM communication system, a mobile station, and an OFDM communication method for performing OFDM data communication by dividing a Frequency band into a plurality of Frequency bands and allocating each Frequency band to a mobile station.

Background

OFDMA access mode

In cellular mobile communication using the OFDM communication scheme, the following Access scheme called OFDMA (Orthogonal Frequency Division Multiple Access) is known: the frequency band is divided into a plurality of frequency bands, and each frequency band is allocated to a plurality of users, thereby multiplexing the users. Fig. 18 is a diagram showing a user division situation of a frequency band with respect to the OFDMA access scheme. In fig. 18 (a), an example is shown in which a band composed of 31 subcarriers is divided into 3 bands composed of 10 subcarriers, 11 subcarriers, and 10 subcarriers, and each band is allocated to a different user.

Case of OFDMA application in downlink

Fig. 19 shows the structure of a base station transmitter to which OFDMA is applied in downlink (communication from a base station to a mobile station), and fig. 20 shows the structure of a mobile station receiver. In the downlink, transmission data of 3 users allocated to each frequency band is allocated to each of the subcarriers 1 to 31 in fig. 18 and input to the IFFT unit 1. The IFFT unit 1 performs IFFT processing on a subcarrier signal, converts the processed signal into a time domain signal, and the Guard Interval insertion unit 2 inserts a Guard Interval (GI: guard Interval) into the time domain signal. Here, as shown in fig. 21, the guard interval GI is obtained by copying the last part of the OFDM symbol. The baseband signal having the GI inserted therein is converted into an analog signal by a DA converter 3a of a transmission circuit (Tx) 3, then converted into an RF signal having a center frequency f1 by a frequency conversion unit 3b, band-limited by a band-pass filter 3c, and then amplified and transmitted from a transmission antenna 4. Fig. 18 (B) shows the bandwidth and the center frequency of each frequency band of the RF signal after frequency conversion , the frequency band having a bandwidth of B1 (MHz) is divided into three frequency bands having a bandwidth of B2 (MHz), and the center frequencies of the respective frequency bands are f0, f1, and f2.

The base station inserts known pilot signals required for the mobile station to perform channel estimation at regular intervals and transmits them in a frame format as shown in fig. 22. The frame is composed of n OFDM symbols, and pilot symbols and control data symbols are inserted into each frame.

The signal transmitted from the transmission antenna 4 is received by the reception antenna 5 (fig. 20) of the mobile station through a fading path, and the reception circuit (Rx) 6 converts the RF signal (fig. 18B) received by the antenna into a baseband signal. That is, the band of the RF signal received by the antenna 5 is limited by the band-pass filter 6a having the bandwidth B1, and then the RF signal is input to the low-noise amplifier 6B, and the low-noise amplifier 6B amplifies the RF signal to a predetermined power. The mixer (mixer) 6c multiplies the local signal having the center frequency of the frequency band of the demodulation object by the output signal of the low noise amplifier 6b, and converts the power-amplified RF signal into a baseband signal. For example, if the demodulation target of the mobile station is band 2, the local oscillator 6d generates a local signal having a frequency f1, and the mixer 6c converts this local signal into a baseband signal by multiplying it by an RF signal. Although the example shown here is a direct conversion from an RF signal to a baseband signal, there is also a method of converting to an intermediate frequency in advance.

As shown in fig. 18B, the baseband-converted signal is passed through an anti-aliasing low-pass filter 6e having a characteristic a of a cutoff frequency B2/2 (MHz), and then input to an AD converter 6f. The AD converter 6f converts the signal into digital data at a sampling rate 2 times the bandwidth B2. Finally, the FIR filter 6g having a cutoff frequency of B2/2 (MHz) intercepts and outputs a signal of a desired frequency band from the AD-converted signal.

The FFT timing synchronization circuit 7 detects FFT timing from the time domain signal including the signal of the desired frequency band output from the reception circuit 6, and the symbol extraction unit 8 extracts a symbol at the FFT timing and inputs the symbol to the FFT unit 9. The FFT unit 9 performs FFT processing on each of the truncated symbols, and converts the processed symbol into a frequency domain subcarrier signal. The channel estimation circuit 10 calculates a correlation between pilot symbols received at a certain interval and a known pilot pattern (pilot pattern) to perform channel estimation for each subcarrier, and the channel compensation circuit 11 compensates for channel variation of data symbols using the channel estimation value. Although the above-described processing demodulates the transmission data allocated to each of the subcarriers 1 to 31 in fig. 18, the OFDMA receiver may demodulate only the subcarrier signal in the frequency band allocated to the own station. In the example of fig. 20, the FFT unit 9 outputs subcarrier signals 11 to 21 on the band 2, and the channel compensation unit 11 performs channel compensation and outputs demodulated data. The information of the frequency band allocated to the own station is notified to the mobile station via a control channel multiplexed in time as in the frame format shown in fig. 22. After that, the demodulated subcarrier signals 11 to 21 are converted into serial data and then decoded, which is not shown in the figure.

Case of OFDMA application in uplink

Fig. 23 is a structural diagram of a mobile station to which OFDMA is applied in an uplink (communication from the mobile station to the base station), and fig. 24 is a structural diagram of the base station.

The frequency bands 1 to 3 shown in fig. 18 (a) are allocated to different mobile stations 20 ₁ ～ 20 ₃ . At each mobile station 20 ₁ ～20 ₃ In the IFFT section 21, the transmission data of the user is input as subcarrier signals 1 to 10, 11 to 21, and 22 to 31 ₁ ～21 ₃ . IFFT unit 21 ₁ ～21 ₃ The sub-carrier signals are subjected to IFFT processing and converted into time domain signals, and the guard interval insertion unit 22 ₁ ～22 ₃ A guard interval GI is inserted into the time domain signal. Transmission circuit (Tx) 23 ₁ ～23 ₃ The input signal is converted into an analog signal, then into an RF signal having center frequencies f0 to f2 corresponding to the respective frequency bands, subjected to band limitation, and then amplified and transmitted from the transmission antenna 24 ₁ ～24 ₃ And sending the message.

The OFDM modulated signal transmitted from each mobile station is received by a receiving antenna 31 (fig. 24) of the base station via each path, and an RF signal is converted into a baseband signal by a receiving circuit (Rx) 32. That is, the band of the RF signal received by the antenna 31 is limited by the band pass filter 32a having the bandwidth B1, and then the limited RF signal is input to the low noise amplifier 32B, and the low noise amplifier 32B amplifies the limited RF signal to a predetermined power. The mixer 32c multiplies the signal having the center frequency f1 of the frequency band B1 output from the local oscillator 32d by the output signal of the low noise amplifier 32B, thereby converting the RF signal after power amplification into a baseband signal. The baseband-converted signal passes through an anti-aliasing low-pass filter 32e having a cutoff frequency of B1/2 (MHz), and is then input to an AD converter 32f. The AD converter 32f converts the signal into digital data at a sampling rate 2 times the bandwidth B1 and outputs the digital data.

The FFT timing synchronization circuit 33 detects FFT timing from the time domain signal including the signal of each frequency band output from the reception circuit 32, and the symbol extraction unit 34 extracts symbols in accordance with the FFT timing and inputs the extracted symbols to the FFT unit 35. The FFT unit 35 performs FFT processing on each of the truncated symbols, and converts the processed symbol into a frequency domain subcarrier signal. The channel estimation circuit 36 calculates a correlation between pilot symbols received at intervals and a known pilot pattern to perform channel estimation for each subcarrier, and the channel compensation circuit 37 compensates for channel variation of data symbols using the channel estimation values. By the above-described processing, the transmission data of 3 users allocated to the subcarriers 1 to 31 in fig. 18 (a) is demodulated. After that, the demodulated subcarrier signals 1 to 31 are converted into serial data, and then each frequency band is decoded, which is not shown in the figure.

Guard band

When the OFDMA access method is applied to the downlink, the mobile station extracts a band allocated to the mobile station by a reception filter (low-pass filter 6e in fig. 20) having a characteristic a as shown in fig. 25 a, and performs reception processing using a receiver (FFT, channel compensation unit, or the like) having a predetermined bandwidth. At this time, the following problems occur: in a region where the band is limited by the reception filter (a sloped region having a frequency attenuation characteristic), the waveform of the subcarriers is distorted, so that orthogonality between the subcarriers is lost, and interference components enter a band of the frequency band.

Therefore, as shown in fig. 25B, guard bands (

subcarriers

10, 11, 21, 22) are provided at band boundaries, and the subcarriers in this region are not used for data transmission, thereby eliminating the influence of the above-described interference. Fig. 25 (C) shows a method of truncating the band 2 by the reception filter at the mobile station. As shown in fig. 25 (C), the inclined portion of the reception filter is designed to be within the guard band region, so that the influence of interference due to waveform distortion can be eliminated. In addition, even when the receiving filter having the wide band-pass characteristic shown in fig. 25 (a) is used, a large interference component is generated in the guard band region, and thus the influence of the interference component entering the band can be prevented.

On the other hand, when OFDMA is applied to the uplink (communication from a mobile station to a base station), the base station receives signals of a plurality of frequency bands collectively and performs OFDM signal processing. Generally, as shown in fig. 21, OFDM has the following structure: a guard interval GI is provided by copying the tail part of the signal waveform and adding the copied tail part to the head of an OFDM symbol, and the orthogonality among subcarriers is still kept for signals with different receiving timings, such as multipath signals and other user signals. This structure will be briefly described with reference to fig. 26. The FFT timing synchronization unit 33 (fig. 24) of the base station measures reception timings (FFT timings) of a plurality of users simultaneously received, extracts a symbol position from the received signal after removing a guard interval of a path (main wave of user 1 in the example of fig. 26) having the earliest FFT timing, and performs FFT processing. In this case, if all user signals are included in the symbol extracted by including the guard interval, orthogonality between subcarriers can be maintained according to the properties of the FFT. However, in the uplink, due to the difference in the distance between the base station and the mobile station or the path state, there is a large difference in the arrival timing of the signal at the base station for each user, and the reception timing difference may exceed the guard interval, resulting in a state where the orthogonality between subcarriers is lost. In this case, as shown in fig. 25 (B), by providing a guard band, the influence of interference due to loss of orthogonality between subcarriers of adjacent bands can be reduced.

In addition, in mobile communication, since a small deviation occurs in the reference frequency between the base station and the mobile station, a carrier frequency is shifted. In general, a mobile station compensates a carrier Frequency offset by an AFC (Automatic Frequency Control), but since the performance of the AFC varies from terminal to terminal, the Frequency offset that cannot be compensated by the AFC varies from user to user. For example, it is known that when the frequency offset is close to one tenth of the subcarrier frequency interval, the transmission characteristics are greatly deteriorated due to the influence of the inter-subcarrier interference. In this case, as shown in fig. 25 (B), by providing a guard band, it is possible to reduce the influence of inter-subcarrier interference generated from a band used by a user with poor AFC performance.

As described above, in the cellular mobile communication system using OFDMA, by providing a guard band, the influence of inter-band interference due to loss of orthogonality between subcarriers can be reduced. However, setting a guard band is to set a frequency band that is not used for communication, which may cause a problem of lowering the frequency utilization efficiency corresponding to the frequency band. In order to improve the frequency use efficiency, it is necessary to use all subcarriers for data transmission without providing guard bands, but as described above, due to the influence of the reception filter, the reception power difference between the frequency bands, the reception timing difference, the frequency offset difference, and the like, and the influence of interference due to the loss of orthogonality between the subcarriers, the throughput cannot be improved, and the frequency use efficiency cannot be improved.

Conventionally, there is a method of using a subcarrier inserted into a guard band region for data transmission (see patent document 1). However, this prior art only shows a method in which when 2 bands are aggregated to be used as 1 band, the guard band region is also used for data transmission, and does not show a method in which it is adaptively determined whether the guard band region is to be used for data transmission or used as a guard band without data transmission.

In view of these problems, an object of the present invention is to adaptively decide whether to use a guard band region for data transmission or to use it as a guard band without data transmission, so that frequency utilization efficiency can be improved.

Patent document 1: japanese laid-open patent publication No. 2002-319917

Disclosure of Invention

In an OFDM communication system for performing OFDM data communication by dividing a frequency band into a plurality of bands and allocating each band to a mobile station, a base station monitors the transmission characteristics of the bands and the use states of adjacent bands, and determines whether a guard band region provided at a band boundary is to be used for data transmission or not to be used for data transmission as a guard band, based on the transmission characteristics of the bands and the use states of the adjacent bands.

For example, in downlink communication, the base station monitors the downlink transmission characteristics of a predetermined band and the use state of an adjacent band received from the mobile station, and determines whether to use a guard band region provided at a band boundary for downlink data transmission or not as a guard band for data transmission, based on the transmission characteristics of these bands and the use state of the adjacent band. Then, the base station notifies the mobile station of the determined method of using the guard band region for downlink communication via control data.

In addition, when performing uplink communication, the base station monitors the transmission characteristics of uplink communication in the band and the use state of the adjacent band, determines whether to use the guard band region provided at the band boundary for uplink data transmission or not as the guard band for data transmission, based on the transmission characteristics of these bands and the use state of the adjacent band, and notifies the mobile station of the use method of the guard band region for uplink communication.

The mobile station demodulates downlink transmission data according to an indication of whether the guard band region is used for data transmission or not in downlink communication by the control information. In addition, according to the instruction of the control information on whether the guard band region is used for data transmission or not in uplink communication, uplink transmission data is allocated to subcarriers of a predetermined frequency band and transmitted.

According to the present invention, it is possible to adaptively determine whether to use a guard band region for data transmission or not as a guard band for data transmission, thereby improving frequency utilization efficiency.

Drawings

Fig. 1 is a diagram illustrating adaptive control of guard bands according to the present invention.

Fig. 2 is a block diagram of a base station apparatus according to the present invention.

Fig. 3 is a configuration diagram of an OFDM transmission unit.

Fig. 4 is a configuration diagram of an OFDM receiving unit.

Fig. 5 is a structural diagram of an FFT timing synchronization circuit.

Fig. 6 is a waveform diagram of a delay profile.

Fig. 7 is a flowchart of a process of determining a method of using a guard band in the uplink guard band control unit.

Fig. 8 is a flowchart of a process of determining a method of using a guard band in the guard band control unit of the downlink.

Fig. 9 is a block diagram of a mobile station.

Fig. 10 is a configuration example of an OFDM receiving section of a mobile station.

Fig. 11 is a configuration example of an OFDM transmission unit of a mobile station.

Fig. 12 is a block diagram of the received power measuring unit.

Fig. 13 is a block diagram of an SIR measuring unit in the vicinity of the guard band.

Fig. 14 is an explanatory diagram of the reception timing measuring unit.

Fig. 15 is a structural diagram of a frequency offset measurement unit.

Fig. 16 is a configuration diagram of the phase difference calculation unit.

Fig. 17 is an explanatory diagram of the frequency offset calculation unit.

Fig. 18 is a diagram showing a user division of a frequency band in the OFDMA access scheme.

Fig. 19 is a configuration diagram of an OFDM transmission unit of a base station.

Fig. 20 is a block diagram of an OFDM receiving unit of a mobile station.

Fig. 21 is an explanatory diagram of guard intervals GI.

Fig. 22 is a frame format explanatory diagram.

Fig. 23 is a configuration diagram of an OFDM transmission unit of a mobile station.

Fig. 24 is a configuration diagram of an OFDM receiving unit of a base station.

Fig. 25 is a diagram illustrating guard bands of an OFDMA access scheme.

Fig. 26 is an explanatory diagram of a structure for maintaining orthogonality between subcarriers.

Detailed Description

(A) Summary of the invention

Adaptive control of guard bands

In OFDMA, there are cases where a guard band is required and cases where a guard band is not required depending on communication conditions such as reception power, reception timing, or frequency offset. In the present invention, the guard band region (

subcarriers

10, 11;21, 22) is adaptively used for data transmission as shown in fig. 1 (a) or the guard band is set as shown in fig. (B) and (C) depending on the communication conditions. This can surely improve the frequency use efficiency.

For example, a mobile station performing data communication at a high transmission rate uses multilevel modulation such as 16QAM or 64QAM or error correction coding at a high coding rate. In this case, the interference due to the loss of orthogonality between subcarriers of adjacent bands is likely to occur. Therefore, a guard band is set when data communication at a high transmission rate is performed, and transmission efficiency is improved (fig. 1B). On the other hand, a mobile station performing data communication at a low transmission rate uses a modulation method such as BPSK or QPSK or error correction coding at a low coding rate. In this case, the influence of interference due to loss of orthogonality between subcarriers of adjacent bands is not so large. Therefore, when data communication at a low transmission rate is performed, a guard band is not provided, and the guard band is also used for data transmission, thereby improving transmission efficiency (fig. 1 (a)). Thus, the protection frequency band is adaptively controlled and set according to the transmission rate of the user, or the protection frequency band region is used for data transmission, thereby improving the frequency utilization efficiency.

Adaptive control of guard bands for the downlink

When signals of each user are allocated to each band for transmission through a downlink, a base station decides whether to use a guard band region for data transmission or not as a guard band for data transmission. Then, information on whether data is to be allocated to the guard band is notified to each mobile station using a control channel. By providing such a configuration, the method of using the guard band can be adaptively controlled. Specifically, the base station performs adaptive control of the guard band in the following manner.

(1) If there is no user to be allocated in a certain frequency band, the base station controls so that the guard band regions at both ends of the frequency band are used for data transmission of respective adjacent frequency bands.

(2) If a transmission rate higher than a predetermined transmission rate is applied to a certain frequency band, the base station performs control such that guard band regions at both ends of the frequency band are used as guard bands and are not used for data transmission (fig. 1 (B)). In addition to the transmission rate, a modulation scheme or a coding rate may be used as a criterion.

(3) The base station may use feedback information from the mobile station as a condition for deciding a method of using the guard band. The mobile station measures the received power of the downlink using the pilot symbols multiplexed in time in each subcarrier of OFDM, and feeds back this information to the base station via the control channel of the uplink. The base station compares the received power of each band fed back, and controls, when the received power difference between adjacent bands is equal to or greater than a predetermined threshold, the guard band region between these bands to be used as a guard band without being used for data transmission (fig. 1 (C)).

(4) The mobile station measures the reception SIR (Signal to Interference Ratio) in the guard band region or in the vicinity of the guard band region using the pilot symbols obtained by multiplexing the time on each subcarrier of OFDM, and feeds back the information to the base station. When the fed-back SIR is equal to or lower than a predetermined threshold, the base station performs control so that the guard band region is used as a guard band and is not used for data transmission (fig. 1 (C)). In addition, the mobile station may determine the method of using the guard band by comparing the measured SIR with a predetermined threshold, and request the base station for the method of using the guard band region.

Adaptive control of the uplink guard band

In the uplink, the base station determines a method of using the guard band region based on the measured information, and instructs the mobile station to use the guard band using a downlink control channel or the like. By providing such a configuration, the method of using the guard band can be adaptively controlled. Specifically, the base station performs adaptive control of the guard band in the following manner.

(1) If a certain frequency band of the uplink has no user to be allocated correspondingly, the base station informs the mobile station to use the guard band regions at both ends of the frequency band for data transmission of adjacent frequency bands.

(2) The base station measures the received power of each uplink band using pilot symbols obtained by multiplexing time on each subcarrier of OFDM, and when the received power difference between adjacent bands is equal to or greater than a predetermined threshold, notifies the mobile station that the mobile station uses the guard band region between these 2 bands as a guard band and does not use it for data transmission (fig. 1 (C)).

(3) If the transmission rate of a certain band allocated to the uplink is higher than a preset transmission rate, the base station informs the mobile station to use the guard band regions at both ends of the band as guard bands without being used for data transmission (fig. 1 (B)). In addition to the transmission rate, the modulation scheme or the coding rate may be used as a criterion.

(4) The base station measures the reception SIR in the guard band region or in the vicinity of the guard band region using the pilot symbols obtained by multiplexing the time on each subcarrier of OFDM, and when the value is equal to or less than a predetermined threshold value, notifies the mobile station that the guard band region is not used for data transmission but is used as the guard band (fig. 1 (C)).

(5) The base station measures the delay curve of each user of the uplink by using the pilot symbol obtained by multiplexing the time in each subcarrier of the OFDM. Then, the reception timing difference of the 2 adjacent bands is compared with the length of the guard interval, and when the timing difference is equal to or greater than a predetermined threshold, the mobile station is notified to use the guard band region between the 2 bands as a guard band without using it for data transmission (fig. 1 (C)).

(6) The base station measures the frequency offset of each user of the uplink by using a pilot symbol obtained by multiplexing time in each subcarrier of the OFDM. Then, the frequency offset difference between the 2 adjacent bands is compared with the subcarrier frequency interval, and when the frequency offset difference is equal to or greater than a predetermined threshold, the mobile station is notified to use the guard band region between the 2 bands as a guard band without using it for data transmission (fig. 1 (C)).

(B) Examples of the embodiments

(a) Base station

Fig. 2 is a block diagram of a base station apparatus according to the present invention, which shows the following: as shown in fig. 1, a frequency band consisting of 31 subcarriers is divided into 3 bands 1 to 3 of 10 subcarriers, 11 subcarriers, and 10 subcarriers, and

users

1,2, and 3 are assigned to the

respective bands

1,2, and 3 to perform OFDM transmission.

The transmission control unit 51 determines a coding rate and a modulation scheme for each user, and inputs the determined coding rate and modulation scheme to the user data modulation/allocation unit 52, the guard band control units 53, andand a control data forming section 55. The user data modulation/allocation section 52 encodes user data at a coding rate instructed for each user from the transmission control section 51, modulates the user data according to an instructed modulation scheme (BPSK, QPSK, 16QAM, etc.), and allocates the user data to the frame generation section 54 of the corresponding band ₁ ～54 ₃ . On the other hand, the guard band control unit 53 controls the frame generation unit 54 to perform control as described later ₁ ～54 ₃ And a control data forming part 55 for notifying whether or not two bands can be used in downlink data transmissionThe case of the side guard band region, in other words, the case of notifying whether guard bands should be set on both sides of the band.

The control data forming unit 55 forms not only data of coding rate or modulation scheme for each user but also data of a method of using a guard band for the downlink and uplink notification bands 1 to 3, and inputs the data to the frame generating unit 54 ₁ ～54 ₃ . The pilot forming unit 56 forms pilots having a pattern corresponding to each frequency band, and each pilot is input to the frame generating unit 54 ₁ ～54 ₃ . Each frame generating section 54 ₁ ～ 54 ₃ Pilot, control data, and transmission data are allocated to predetermined subcarriers 1 to 31 at timings shown in the frame format in fig. 22.

When it is instructed to use the guard band region (subcarrier 10) of band 1 as the guard band, the frame generation unit 54 ₁ According to the frame format, when the sub-carriers 1 to 9 are allocated pilot symbols of band 1, control data symbols of band 1, and transmission data symbols of band 1, and it is instructed that the guard band region can be used for data transmission, the frame generation unit 54 ₁ These symbols are allocated to subcarriers 1 to 10 according to the frame format.

In the case where it is instructed to use the guard band region (subcarriers 11 and 21) of band 2 as the guard band, the frame generation section 54 ₂ The sub-carriers 12 to 20 are allocated pilot symbols of band 2, control data symbols of band 2, transmission data symbols of band 2 according to the frame format,when instructed that the guard band region can be used for data transmission, the frame generation unit 54 ₂ These symbols are allocated to subcarriers 11-21 according to the frame format. In addition, in the case where it is instructed that one guard band region (subcarrier 11) is used as a guard band and the other guard band region (subcarrier 21) is available for data transmission, the frame generation part 54 ₂ According to the frame format, sub-carriers 12 to 21 are allocated pilot symbols of band 2, control data symbols of band 2, and transmission data symbols of band 2.

When it is instructed to use the guard band region (subcarrier 22) of band 3 as the guard band, the frame generation unit 54 ₃ According to the frame format, sub-carriers 23 to 31 are allocated pilot symbols of frequency band 3, control data symbols of frequency band 3, and transmission data symbols of frequency band 3, and when it is instructed that the guard band region can be used for data transmission, frame generation unit 54 ₃ These symbols are allocated to subcarriers 22-31 according to the frame format.

The OFDM transmission unit 57 has the configuration shown in fig. 3, and operates in the same manner as described with reference to fig. 19. That is, the IFFT unit 57a generates the slave frame 54 ₁ ～54 ₃ Input subcarrier signalNos. 1 to 31 are subjected to IFFT processing and converted into time domain signals, the guard interval insertion section 57b inserts a guard interval GI into the time domain signals, and the transmission section 57c converts the baseband signals output from the guard interval insertion section 57b into RF signals having a center frequency f1 and transmits the RF signals from the transmission antenna 58.

The OFDM modulated signal transmitted from each mobile station is received by a reception antenna 61 of the base station via each path, and is input to an OFDM reception unit 62. The OFDM receiving section 62 has a configuration as shown in fig. 4, and its operation is the same as that described in fig. 24. That is, the receiving circuit 62a converts the RF signal into a baseband signal, the FFT timing synchronization circuit 62b detects FFT timing from a time domain signal including signals of respective frequency bands output from the receiving circuit 62a, and the symbol extraction unit 62c extracts a symbol in accordance with the FFT timing and inputs the symbol to the FFT unit 62d. The FFT unit 62d performs FFT processing on each of the extracted symbols, and converts the processed symbols into frequency domain subcarrier signals 1 to 31. The channel estimation circuit 62e calculates a correlation between pilot symbols received at a certain interval and a known pilot pattern to perform channel estimation for each subcarrier, and the channel compensation circuit 62f compensates for channel variation of data symbols using the channel estimation value.

Fig. 5 is a block diagram of an FFT timing synchronization circuit 62b having a correlation operator 62b that operates the correlation between the received signal and the pilot symbol replica (known) of each user ₁ ～62b ₃ And a fastest path detection unit 62b for detecting the fastest path according to the frequency bands 1 to 3 ₄ . The FFT timing synchronization circuit 62b calculates a delay profile for each user (see fig. 6) based on the correlation operation between the pilot symbol replica for each user and the received signal, detects the timing of the fastest path, that is, the initial timing of the rising edge timing t1 to t3 at which the delay profile is equal to or greater than a threshold value, and inputs the detected timing to the symbol slicer 62c as the FFT timing.

Returning to fig. 2, the ofdm reception unit 62 decodes the downlink transmission characteristic data transmitted from the mobile station via the control channel, inputs the decoded data to the guard band control unit 53, and inputs the channel estimation values and delay profiles (fig. 6) of the subcarriers 1 to 31 to the measurement circuits 63 of the bands 1 to 3 ₁ ～63 ₃ In (1). The downlink transmission characteristic data refers to downlink reception power and reception SIR of subcarriers in or near the guard band region.

Measuring circuit 63 for each frequency band ₁ ～63 ₃ The transmission characteristics of the uplink frequency bands 1 to 3 are measured and input to the guard band control unit 53. Namely, a measuring circuit 63 ₁ ～63 ₃ Includes a received power measuring part PWM for measuring the uplink received power of each frequency band, and a protector for measuring each frequency bandSIR measuring unit SIM for measuring reception SIR of sub-carrier in the vicinity of a band, reception timing measuring unit RTM for measuring symbol reception timing of each band, and reception control unit RTM for controlling reception SIR of sub-carrier in each bandA frequency offset measuring unit FOM for measuring the frequency offset of each band inputs the measured uplink received power, uplink received SIR, reception timing, and frequency offset to the guard band control unit 53. The structure of each measuring section will be described later.

The guard band control unit 53 controls the measurement circuits 63 according to the use state of the band inputted from the transmission control unit 51 ₁ ～63 ₃ The input uplink transmission characteristics and the downlink transmission characteristics input from the OFDM reception unit 62 are used to determine whether or not guard band regions on both sides of each band can be used for downlink data transmission, that is, whether or not guard bands should be provided on both sides of the band, for each of the uplink and downlink, and to notify the frame generation unit 54 of the result ₁ ～54 ₃ And a control data forming section 55.

(b) Processing for determining method of using protection frequency band

Fig. 7 is a flowchart of the process of the uplink guard band control unit 53 determining the method of using the guard band.

The guard band control unit 53 determines whether or not a user (mobile station) is allocated to each band (step 101), and if there is a band to which a user is not allocated, determines that guard band regions on both sides of the band are to be used for data transmission in an adjacent band (step 102). Referring to fig. 1 (B), the guard band region is

subcarriers

10, 11; 21. 22. Thus, for example, if no user is allocated to band 2, then it is decided that band 1 subcarriers 10 are to be used for data transmission and band 3 subcarriers 22 are to be used for data transmission.

Next, the guard band control unit 53 checks whether or not there is a data communication party performing a data communication with a high transmission rate, with reference to the transmission rate, modulation scheme, or coding rate (step 103). If so, it is decided not to use the guard band regions on both sides of the band for data transmission (step 104). For example, if the transmission rate of band 2 is high, it is decided not to use the subcarrier 10 of band 1 for data transmission, to use the

subcarriers

11 and 21 of band 2 for data transmission, and to use the subcarrier 22 of band 3 for data transmission.

Next, the guard band control unit 53 compares the uplink received power of each band, checks whether there is a large difference in the received power between adjacent bands (step 105), and if so, determines not to use the subcarriers in the guard band region located on the boundary between adjacent bands for data transmission (step 106).

After the judgment processing of steps 105 and 106 is finished, it is checked whether or not the reception SIR of the guard band region of each band of the uplink is large (step 107), and if the reception SIR is large, it is decided that subcarriers near the guard band region are to be used for data transmission, and if the reception SIR is small, it is decided that they are to be used as a guard band (step 108).

Next, the guard band control unit 53 checks whether or not the reception timing difference of the adjacent band in the uplink is larger than a predetermined threshold (step 109), and if so, determines not to use the guard band region located on the boundary of the adjacent band for data transmission (step 110).

Finally, the guard band control unit 53 checks whether or not the frequency offset difference between the adjacent bands in the uplink is larger than a predetermined threshold (step 111), and if so, determines not to use the guard band region located on the boundary of the adjacent bands for data transmission (step 112), and then ends the processing. The guard band control unit 53 then repeats the above-described processing for each frame.

Fig. 8 is a flowchart of a process in which the downlink guard band control unit 53 determines a method of using a guard band, and steps 201 to 204 are the same as the processes of steps 101 to 104 in fig. 7.

After the processing in

steps

203 and 204 is completed, the guard band control unit 53 compares the downlink reception power included in the information (feedback information) notified from each mobile station, checks whether there is a large difference in the reception power between adjacent bands (step 205), and if there is a difference, determines not to use the subcarriers of the guard band region located on the boundary between adjacent bands for data transmission (step 206).

Next, the guard band control unit 53 checks whether or not the reception SIR in the vicinity of the guard band region of each downlink band included in the feedback information notified from each mobile station is large (step 207), and determines to use the sub-carriers of the guard band region for data transmission if the reception SIR is large, and determines to use the sub-carriers as the guard band if the reception SIR is small (step 208). The guard band control unit 53 then repeats the above-described processing for each frame.

(c) Mobile station

Fig. 9 is a block diagram of a mobile station on which it is assumed that a frequency band 2 is allocated.

A signal transmitted from the base station is received by a reception antenna 71 of the mobile station via a fading path, and the received signal is input to an OFDM reception unit 72.

The OFDM receiving section 72 has a configuration as shown in fig. 10, and its operation is the same as that described in fig. 20. That is, the receiving circuit (Rx) 72a outputs, for example, a baseband signal of the frequency band 2 based on the RF signal received by the antenna 71. The FFT timing synchronization circuit 72b detects FFT timing from the time domain signal including the signal of the band 2 output from the reception circuit 72a, and the symbol extraction unit 72c extracts a symbol in accordance with the FFT timing and inputs the symbol to the FFT unit 72d. The FFT unit 72d performs FFT processing on each of the extracted symbols, and converts the processed symbols into frequency domain signals of the frequency band 2, i.e., subcarrier signals 11 to 21.

Returning to fig. 9, the channel estimation circuit 73 calculates the correlation between pilot symbols received at regular intervals and a known pilot pattern, performs channel estimation on the subcarriers 11 to 21, the control channel demodulation unit 74 demodulates the control channel using the channel estimation value to find the guard band usage method for the downlink and uplink band 2, notifies the data channel demodulation unit 75 of the guard band usage method DLGB for the downlink, and notifies the frame generation unit 76 of the guard band usage method ULGB for the uplink.

The data channel demodulation unit 75 demodulates the data channel using the channel estimation value, and outputs demodulated data according to the guard band usage DLGB of the downlink. For example, if the

subcarriers

11 and 21 of the guard band region are used as the guard band, the demodulated data of the subcarriers 12 to 20 are output, and if the

subcarriers

11 and 21 are used for data transmission, the demodulated data of the subcarriers 11 to 21 are output.

The measurement circuit 77 measures the downlink reception power PW and the reception SIR of the sub-carrier in the guard band region or in the vicinity of the guard band region using the channel estimation value, and inputs the measured values to the frame generation unit 76.

The frame generator 76 allocates pilot symbols, control data symbols including downlink reception power PW and reception SIR, and transmission data symbols to the subcarriers 11 to 21 of the band 2 according to the frame format of fig. 22, and inputs the allocated pilot symbols, control data symbols including the downlink reception power PW and reception SIR, and transmission data symbols to the OFDM transmitter 78, in accordance with the uplink guard band usage ULGB notified from the control channel demodulator 74. That is, if the frame generation unit 76 is instructed to use the guard band region of band 2 as the guard band, pilot symbols, control data symbols, and transmission data symbols are allocated to the subcarriers 12 to 20 in accordance with the frame format, and if it is instructed that the guard band region is available for data transmission, these symbols are allocated to the subcarriers 11 to 21 in accordance with the frame format and input to the OFDM transmission unit 78.

The OFDM transmission unit 78 has the structure shown in fig. 11. The IFFT section 78a performs IFFT processing on the subcarrier signals 11 to 21 to convert them into time domain signals, the guard interval insertion section 78b inserts a guard interval GI into the time domain signals, the transmission circuit (Tx) 78c converts the input signals into baseband signals, then frequency-converts them into RF signals corresponding to the band 2 with the center frequency f1 to perform band limitation, amplifies them, and then transmits them from the transmission antenna 79.

(d) Measuring circuit

Fig. 12 is a block diagram of the received power measuring unit PWM of fig. 2, which can also be used for the received power measurement of the measuring circuit 77 of fig. 9.

The channel estimation unit 62e outputs a channel estimation value h of the amount of subcarriers constituting the frequency band _i ＝H _i ×exp(jθ _i ) (i =1 to n), the power calculating unit 81a squares the amplitude | h _i | ² The power of each subcarrier is calculated, and the totalizing unit 81b uses the following equation:

P＝∑ _i |h _i | ² (i＝1～n)(1)

the total power P of the frequency band is calculated.

Fig. 13 is a block diagram of the guard band vicinity SIR measuring unit SIM in fig. 2, which can also be used for guard band vicinity SIR measurement by the measurement circuit 77 in fig. 9.

The average value calculation section 85b calculates an average value m of the subcarrier signals of N symbols, and the desired wave power calculation section 85c calculates m by squaring and adding the I, Q axis components of the average value m ² (power S of the desired signal). The reception power calculating section 85d calculates the I-axis component H of the subcarrier signal _I And Q-axis component H _Q Squared and added, i.e. calculated as P = H _I ² +H _Q ² The received power P is calculated, the average value calculating section 85e calculates the average value of the received power, and the subtractor 85f subtracts m from the average value of the received power ² The SIR calculating unit 85g outputs interference power I (desired power S), and uses the desired power S and the interference power I according to the following equation:

SIR＝S/I (2)

to calculate the SIR. When an input signal including a desired signal and an interference wave is xi (i =1,2.. N), an average value m of the input signal is calculated by the following formula: m = (1/N) · ∑ xi (i =1,2.. N), and the desired wave power S is obtained by squaring the average value m. On the other hand, the average (variance) σ obtained by squaring the difference between the input signal and the average ² Is interference wave power I, which is calculated by the following formula: sigma ² ＝(1/N)·∑(xi-m) ² (i =1,2.. N). Transforming the above formula to obtain:

σ ² ＝(1/N)·∑|xi| ² (2m/N)·∑xi+(1/N)·∑m ²

＝(1/N)·∑|xi| ² -2m ² +m ²

＝[(1/N)·∑|xi| ² ]-m ² (3)

therefore, the received power calculation unit 85d and the average value calculation unit 85e perform the calculation of the 1 st term on the right side of the expression (3), and the subtractor 85f subtracts m from the output of the average value calculation unit 85e ² (desired wave power S)The interference power I is output, and the SIR calculating unit 85g performs the calculation of the equation (2) to output the SIR.

Fig. 14 is an explanatory diagram of the reception timing measurement unit RTM of fig. 2, and the same components as those in the configuration of fig. 5 are denoted by the same reference numerals. The correlation calculator 62b of the FFT timing synchronization circuit 62b is input to the reception timing measurement unit RTM ₁ ～62b ₃ The delay profile (see fig. 6) to be output is measured as reception timing from each user at rising edge timings t1 to t3 where each delay profile is equal to or greater than a threshold value.

Fig. 15 is a structural diagram of the frequency offset measurement unit FOM of fig. 2, and shows frequency offset measurement units FOM of frequency bands 1 to 3, respectively. The frequency deviation measuring part FOM of each frequency band respectively calculates the channel estimation value h of each subcarrier _n The frequency deviation amount f is obtained from the average value of the phase change amounts of (2) _offset . Since the subcarriers for each user are determined, the frequency offset amount for each user can be found. Since the frequency offset measurement units of the respective bands have the same configuration, only the frequency offset measurement of the band 1 will be described.

Channel estimation unit 62e from frequency band 1 ₁ Channel estimation values h of subcarriers 1-10 ₁ ～h ₁₀ Phase difference calculation unit 91 that inputs the phase difference to the frequency offset measurement unit ₁ ～91 ₁₀ . Phase difference calculation unit 91 ₁ ～ 91 ₁₀ As shown in fig. 16, the delay circuit 92 and the phase difference calculation unit 93 are provided, and the channel estimation value h in the period T of the pilot insertion interval is inserted ₁ ～h ₁₀ The respective phase changes are detected as offset frequencies. That is, when there is an offset between the reference frequency of the base station and the frequency of the user (mobile station), the phase of the channel estimation value is deviated,the larger the offset, the larger the phase deviation. Therefore, the delay part 92 delays the channel estimation value h in the pilot period _n Delay/phase difference calculation unit 93 calculates and outputs delayed channel estimation value h _n (T-T) and the current channel estimate h _n Phase difference between (t): delta theta = ≈ h _n (t)-∠h _n (T-T). Frequency offset calculation unit 94 ₁ As shown in fig. 17, the offset frequency of the frequency band 1 is calculated using the average value of the frequency offset of each subcarrier according to the following equation:

the

other frequency bands

2 and 3 may also calculate the offset frequency according to the same manner.

The above description has been made for the case where the number of subcarriers is 31 and the number of frequency bands is 3, but it is apparent that the present invention is not limited to these numbers.

As described above, according to the present invention, by adaptively controlling the method of using the guard band region, it is possible to effectively use the frequency band and improve the frequency use efficiency. In addition, the base station adaptively controls the use/non-use of the guard band region according to the path characteristics, the feedback information of the mobile station, and the use state of the adjacent band, thereby improving the throughput of the system.

Claims

1. An OFDM communication method for performing OFDM data communication by dividing a frequency band into a plurality of bands and allocating each band to a mobile station, the OFDM communication method comprising:

monitoring the transmission characteristics of the frequency band and the use state of the adjacent frequency band; and

according to the transmission characteristics of these bands and the use status of the adjacent bands, it is determined whether the guard band region located at the band boundary is to be used for data transmission or not to be used for data transmission as the guard band.

2. An OFDM communication method for performing OFDM data communication by dividing a frequency band into a plurality of bands and allocating each band to a mobile station, the OFDM communication method comprising:

monitoring a downlink transmission characteristic received from a mobile station and a use state of an adjacent frequency band; and

according to the transmission characteristics of these bands and the use states of adjacent bands, it is determined whether a guard band region located at the band boundary is to be used for downlink data transmission or not as a guard band for data transmission.

3. The OFDM communication method of claim 2, wherein the base station notifies the mobile station of a usage method of the guard band region of the downlink communication through the control data.

4. An OFDM communication method for performing OFDM data communication by dividing a frequency band into a plurality of bands and allocating each band to a mobile station, the OFDM communication method comprising:

monitoring the transmission characteristics of uplink communication of the frequency band and the use state of the adjacent frequency band;

according to the transmission characteristics of the frequency bands and the using states of the adjacent frequency bands, determining whether a guard band region arranged at the boundary of the frequency bands is used for data transmission of an uplink or is used as the guard band without being used for data transmission; and

the method of using the guard band region for uplink communication is notified to the mobile station.

5. The OFDM communication method of claim 4, wherein the mobile station transmits data to the base station according to an indication of a usage method of the guard band region.

6. The OFDM communication method as claimed in claim 2 or 4, wherein when there is no user to be allocated for a certain frequency band, the base station uses guard band regions at both ends of the frequency band for data transmission of respective adjacent frequency bands.

7. The OFDM communication method as claimed in claim 2 or 4, wherein when data communication at a high transmission rate is performed in a certain frequency band, the base station decides not to use the guard band regions at both ends of the frequency band for data transmission.

8. The OFDM communication method as claimed in claim 2 or 4, wherein in the case where the difference in the reception power of the adjacent bands is large, the base station decides not to use the guard band region at the boundary of the adjacent bands for data transmission.

9. The OFDM communication method as claimed in claim 2 or 4, wherein the base station decides not to use the guard band region for data transmission in case that the reception SIR of sub-carriers near the guard band is small.

10. The OFDM communication method of claim 4, wherein the base station decides not to use a guard band region at the boundary of adjacent bands for data transmission in the case where the difference in reception timing between adjacent bands is large.

11. The OFDM communication method of claim 4, wherein in case that the frequency offset difference of adjacent bands is large, the base station decides not to use a guard band region at the boundary of the adjacent bands for data transmission.

12. A base station for an OFDM communication system that performs OFDM data communication by dividing a frequency band into a plurality of bands and allocating each band to a mobile station, the base station comprising:

an information receiving unit that receives feedback information from a mobile station, the feedback information being information on transmission characteristics of downlink communication;

a monitoring unit that monitors the use state of the adjacent frequency band;

a measurement unit that measures transmission characteristics of each frequency band of uplink communication; and

and a band control unit which determines whether to use a guard band region set at a band boundary for data transmission or to use the guard band region as a guard band for data transmission, based on feedback information from the mobile station, a use state of an adjacent band, and transmission characteristics of a band.

13. The base station of claim 12, comprising an OFDM transmitting section which allocates data transmitted through the respective bands to subcarriers and OFDM-transmits them according to whether the guard band region is to be used or not used in downlink communication.

14. The base station of claim 13, wherein the OFDM transmission section notifies a mobile station of a method of using a guard band region for downlink communication by control data.

15. The base station of claim 12, wherein the OFDM transmission section notifies a mobile station of a method of using a guard band region for uplink communication by control data.

16. A mobile station for an OFDM communication system that performs OFDM data communication by dividing a frequency band into a plurality of bands and allocating each band to the mobile station, the mobile station comprising:

an OFDM reception unit which receives downlink transmission data and control information from a base station via a predetermined frequency band;

a measurement unit that measures transmission characteristics of downlink communication;

an OFDM transmission unit that transmits the measured transmission characteristics to a base station;

a control information demodulation unit that demodulates control information transmitted from the base station; and

and a data demodulation unit which demodulates the downlink transmission data in accordance with an instruction of the control information as to whether the guard band region is to be used for data transmission or not in the downlink communication.

17. The mobile station of claim 16, wherein said OFDM transmission section has means for performing: and allocating uplink transmission data to the sub-carriers of the prescribed band and transmitting the same according to the indication of the control information on whether the guard band region is to be used for data transmission or not in uplink communication.